The present invention relates generally to wireless electromagnetic-wave communications, and particularly to interferometry and parallel signal-processing techniques that enhance bandwidth efficiency and reduce complexity of transmitters and receivers.
Wireless communications includes a large number of applications that service a wide variety of communication needs. Different communication markets are characterized by different transmission protocols and frequency bands. These markets are encumbered by technology fragmentation resulting from competitors who have a vested interest in promoting their own proprietary transmission protocols and signal-processing technologies. This fragmentation impedes compatibility between different applications and systems, reduces bandwidth efficiency, increases interference, and limits the usefulness of wireless communications. Thus, there is an overwhelming need to unify these technologies.
Throughout history, the quest to understand the universe has focused on discovering the elementary components of the universe. Knowledge of the properties of fundamental elements can provide an understanding of the properties of complex combinations of those elements. From an engineering perspective, the properties of a complex combination of elements are determined by properties of the elements and the manner in which the elements are combined.
Many aspects of conventional Quantum theory, as well as more recent discoveries in high-energy physics, indicate that a wave-based phenomena is the fundamental basis of all matter and energy. Quantum theory also describes a complex state as a superposition between component waveforms, the superposition resulting from constructive and/or destructive interference between the waveforms.
The idea of using multiple low-rate communication channels to transmit a large amount of data is well known. U.S. Pat. No. 5,960,032 describes dividing a high-rate data stream into a plurality of parallel low-rate bit streams that are each modulated with a direct-sequence spreading code. Other methods of multicarrier processing are described in U.S. Pat. No. 6,061,405 and U.S. Pat. No. 5,729,570. Although several prior-art methods involve redundantly modulating multiple component waveforms, none of these methods achieve the benefits of the present invention that are enabled by interferometrically combining the waveforms. For example, U.S. Pat. Nos. 5,519,692 and 5,563,906 describe geometric harmonic modulation (GHM) in which preamble and traffic waveforms are created from multiple carrier frequencies (tones). GHM waveforms comprise tones incorporating a binary phase code where signal phases are 0 or xe2x88x92xcfx80/2. The binary phase offsets, which are applied to the tones, provide the spreading codes. Orthogonality of GHM signals is realized upon correlation with a reference signal at a receiver. A preamble carrier waveform is constructed by summing the tones. Therefore, the preamble signals are similar to Multicarrier CDMA (MC-CDMA) signals.
Each receiver monitors the preamble signals for its own phase code and then despreads and decodes the appended traffic waveforms. The traffic waveforms are products of the tones. The receiver generates a reference waveform from a product of tones having phase offsets that correspond to the receiver""s phase code. The reference waveform is correlated with the received signals to produce a correlation result that is integrated over the data-bit duration and over all tones.
GHM uses binary phase offsets instead of incremental poly-phase offsets. Thus, GHM does not provide carriers with phase relationships that enable the superposition of the carriers to have narrow time-domain signatures. Consequently, received GHM signals require processing by a correlator, whereas signals that are orthogonal in time can be processed using simpler signal-processing techniques, such as time sampling and weight-and-sum. Furthermore, GHM does not achieve the capacity and signal-quality benefits enabled by time-orthogonal signals.
U.S. Pat. No. 4,628,517 shows a radio system that modulates an information signal onto multiple carrier frequencies. Received carriers are each converted to the same intermediate-frequency (IF) signal using a bank of conversion oscillators. The received signals are then summed to achieve the benefits of frequency diversity. In this case, frequency diversity is achieved at the expense of reduced bandwidth efficiency. The process of converting the received signals to the same frequency does not allow orthogonality between multiple information signals modulated on the same carriers.
In order to accommodate the processing speeds of conventional signal-processing techniques, high-frequency carrier signals are typically down converted to an IF before demodulation. In conventional receivers, components in the IF sections comprise the majority of components of the receiver.
Conventional down converters include electrical components whose properties are frequency dependent. Consequently, conventional down converters are designed to operate at specific frequencies or frequency bands and do not have flexibility to adapt to different frequencies.
Conventional down converters employ mixers, which generate undesired intermodulation and harmonic products. Filters are needed to remove the undesired signals. Such filters reduce the power level of the modulated carrier signals and, thus, require amplifiers and additional power sources for the amplifiers.
It is preferable to reduce the number of filters and mixers in a wireless system because these components attenuate desired signals and require additional low-noise amplifiers to compensate for the reduced signal strength. Low-noise amplifiers require substantial power to operate. High-frequency amplifiers typically require more power than low-frequency amplifiers. In a portable system, such as a cellular telephone, low-noise amplifiers use a substantial portion of the system""s power.
Since many radio-frequency (RF) components, such as amplifiers, filters, and impedance-matching circuits are highly frequency dependent, receivers that are designed for one frequency band are usually not suitable for applications that make use of other frequency bands. Similarly, receivers designed for a particular transmission protocol are typically not adaptable to other protocols. Furthermore, receivers are typically not adaptable to variations of the protocol for which they are designed.
Conventional receiver components are typically positioned over multiple integrated-circuit (IC) substrates to accommodate processing in RF, IF, and baseband frequencies. Receivers that use multi-mode processors (i.e., processors having separate systems designed to process different transmission protocols) use multiple ICs. Additional signal amplification is often required when bridging multiple chips. Thus, the use of multiple substrates introduces additional costs beyond the costs associated with producing the ICs.
What is needed is an underlying signal architecture and signal-processing method that not only enhances signal quality and system capacity, but also simplifies transmission and reception of communication signals. Accordingly, it is desirable that a proposed signal-processing method eliminate the need for IF processing and, thus, substantially reduce the number of components in a receiver. It is preferable that a proposed signal-processing technique enable parallel processing, adaptability to different frequency ranges, compatibility with different transmission protocols, interference mitigation, and reduced distortion.
In commercial telecommunication systems, it is well known that technology complexity leads to higher manufacturing costs, reduced reliability, and longer development cycles. For example, while IS-95 provided the highest spectrum efficiency of second-generation mobile systems, it also incurred higher costs and a longer development time to provide forward error correction, Rake receivers, power control, and soft handoff. Accordingly, it is preferable that a proposed communication system enable simple signal-processing methods and systems for transmission and reception. It is only through a simple, yet elegant signal processing technique that all of the needs discussed herein can be addressed without compromise.
The present invention is directed to systems and methods for transmitting and receiving Carrier Interferometry (CI) signals, such as CIMA (also known as multicarrier interferometry) signals. The frequency spectrum of an electromagnetic signal illustrates the relative amplitudes of sine waves that, when summed together with the correct phase, reconstruct the signal in the time domain. A time-limited signal may have an infinite number of discreet sinusoidal frequency components. However, modulating the sinusoidal components provides a finite number of continuous-spectrum components. The time-domain representation of an electromagnetic signal can be constructed by generating a plurality of sine waves that implement the relative amplitudes and phases contained in the frequency spectrum of the electromagnetic signal.
CI uses a baseband information signal to redundantly modulate a plurality of carrier signals. A superposition of the carriers produces a baseband-frequency envelope that represents the information signal. Controlling the relative amplitudes, phases, and/or frequencies of individual carrier signals produces a superposition signal having a desired time-domain profile.
In xe2x80x9cQuantum theory, the Church-Turing principle and the universal quantum computer,xe2x80x9d David Deutsch describes Quantum theory as a xe2x80x9ctheory of parallel interfering universes.xe2x80x9d CI manipulates fundamental wave components to create constructive and destructive interference zones from which desired communication signals are created. The benefits of CI include unprecedented bandwidth efficiency, superior signal quality, exceptional interference rejection, diversity benefits, reduced power requirements, adaptability to any wireless or waveguide transmission protocol, parallel processing, direct down-conversion, and direct up-conversion.
The reception method of the invention makes use of the diversity and robustness of CI to substantially reduce interference and distortion that occurs in a communication channel. Furthermore, information signals recovered from the superposition of multiple carriers are highly insensitive to phase jitter, frequency distortions, and timing offsets.
The initial market for the Carrier Interferometry Underlying Architecture is communication infrastructure. Applications include mobile wireless systems, fixed-point wireless local loop, smart antennas, voice-over-IP, secure communications, very high-bit-rate digital subscriber line, and communications applications that have traditionally used reprogrammable devices such as digital-signal processing (DSPs) and FPGAs. Objectives of the present invention""s methods and systems are summarized by the following description of attributes and embodiments:
A method and system for transmitting electromagnetic signals that is easily adaptable to any wireless transmission protocol.
A method and system for receiving electromagnetic signals that is easily adaptable to any wireless transmission protocol.
A method and system for providing an underlying multicarrier architecture that substantially improves the quality and increases the capacity of any wireless protocol.
A method and system for providing wireless communications with an underlying signal architecture that enables simple designs for transmitters and receivers.
A method and system that uses slow, parallel signal-processing techniques to transmit and receive wideband and ultra-wideband communication signals.
A method and system that enables spatial multiplexing without antenna arrays.
A method and system that exploits multipath effects to enhance spatial multiplexing.
A method and system that provides diversity benefits of a spread-spectrum system to narrowband communication protocols, such as TDMA.
A method and system that provides narrowband-processing benefits, such as enhanced array-processing capabilities, to wideband and ultra-wideband communication protocols.
A method and system that provides an underlying signal architecture that enables sub-spatial overlay procedures (such as spatial interferometry multiplexing) to provide unprecedented bandwidth efficiencies to all communication protocols.
A method and system that exploits dispersive and other nonlinear waveguide characteristics to enhance the capacity of waveguide communications.
A method and system that enables a seamless conversion between waveguide and wireless transmission protocols.
A method and system for directly down converting modulated carrier signals to demodulated baseband signals.
A method and system for improving energy transfer of an under sampling process.
A method and system employing under sampling to down convert modulated carrier signals in which the method and system are substantially insensitive to carrier frequency drifts and offsets, such as Doppler shifts and transmitter-frequency instability.
A method and system for down converting electromagnetic signals that is easily adapted to different frequencies.
A method and system for down converting electromagnetic signals that is adaptable to any transmission protocol.
A method and system for down converting electromagnetic signals using a local-oscillator frequency that is substantially lower than the carrier frequency.
A method and system for down converting electromagnetic signals using a low sampling frequency and a simple anti-aliasing filter.
A method and system for down converting electromagnetic signals that uses fewer filters than conventional down converters.
A method and system for down converting electromagnetic signals that uses less power than conventional down converters.
A method and system for down converting electromagnetic signals that uses fewer components than conventional down converters.
A method and system for down converting electromagnetic signals that can be implemented on an integrated circuit.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail with reference to the accompanying drawings.